This relates to solid-state image sensor arrays and, more particularly, to image sensors with temperature sensor pixels for performing dark current compensation.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels. The image pixels generate image signals in multiple color channels. Readout circuitry such as analog-to-digital converter circuits are commonly coupled to the image pixels for reading out image signals from the image pixels.
In an image sensor, the temperature of the image sensor substrate typically affects the image signals generated by the image pixels. In a typical pixel photodiode, there is some current (i.e., dark current) in the photodiode even when no light is incident upon the photodiode (due to the inherent movement of electrons across the corresponding semiconductor junction). As the temperature of the photodiode increases, this flow of the electrons, and therefore the dark current, increases. Increased dark current in the image sensor can cause excessive and unsightly noise in the final image signal.
Because the level of dark current generated by a photodiode is temperature-dependent, it is useful to be able to detect the temperature of the image sensor array so that dark current contributions to the final image signal can be compensated for. In some conventional image sensors, a junction sensor is placed on the image sensor substrate separated from the pixel array. However, the junction sensor can only measure the temperature of the image sensor array substrate at the location at which the junction sensor is placed, resulting in a single temperature reading that is representative of one location on the image sensor. The image sensor then uses this temperature reading to generate a correction value for correcting for temperature-based dark current in the captured image signals. However, in this scenario, the correction value will inaccurately estimate the temperature and corresponding dark current signal contribution for pixels at positions on the substrate that are far from the junction sensor.
It would therefore be desirable to provide imaging devices with improved systems and methods for detecting array temperatures and compensating for dark current in the array.